Performancetuning with Multiprocessor and Parallelism

I have Informix-Online 7.13 on a SUN (2 Processors). Does anyone has experience with the usage of multiprocessor environment (parameter MULTIPROCESSOR in onconfig)? I use the option single-processor. Are there any traps using more than one processor? In former Releases, Informix had some trouble with parallel database queries. Sometimes the results have been wrong. Does anyone know, if these bugs are fixed in this Version? Is there any suggestion for the onconfig-parameter for this chapter? thanks Roland